By 466 B.C. Athens completely controlled the Delian League. The treasury, formerly housed at Delos, was moved to Athens where much of the funds were used by Pericles for his building projects. Attempts to break away from the League, such as Naxos c. 471 B.C. and Thasos in 465 B.C., were crushed.
Starting in 459 B.C. Athens came into a series of conflicts with Corinth, an ally of Sparta as a result of her expansions westward. This instigated the First Peloponnesian War, which lasted from 457-446 B.C. The result was the formation of two rival camps: The Peloponnesian League headed by Sparta, and Athens and her allies.
The Second Peloponnesian War began in 431 B.C. when Athens forced Potidaea, a colony of Corinth, to join the Delian League. Potidaea appealed to Corinth for assistance, who eventually persuaded Sparta to aid them against Athens. Sparta marched an army into Attica in 431 B.C.
The two opposing cities could not have been more dissimilar. Athens aimed to win the war by naval power, while Sparta was determined to win on land. Athens adopted the strategy of refusing to engage Sparta in a decisive land battle and to expand by sea. Initially Sparta marched their armies into Attica and devastated the countryside. The Athenians would withdraw behind their walls to avoid confrontation with the superior Sparta hoplites. On the sea, however, Athens dominated Sparta's coasts. Neither side was able to strike a crippling blow.
In 430 B.C. Athens was stricken down by another enemy: plague. The plague struck Athens killing about 1/3 of her population. In 429 B.C. the plague took the life of Athen's brilliant statesman, Pericles. With Pericles gone his successors attempted to wage the war on land and sea. Three confrontations followed. The first in 425 B.C. at Sphacteria at which Athens defeated Sparta. The second in 424 B.C. at Delium at which Athens was decisively beaten by the Boeotians. The third occurred at Amphipolis in 422 B.C. During this engagement Cleon, the Athenian leader, and Brasidas, a Spartan commander, were killed. A temporary halt to the fighting was called soon afterwards in 421 B.C.
It was not long before hostilities were renewed. In June 415 B.C. Athens sent a force to Syracuse in Sicily. The goal was to interrupt the corn trade to the Peloponnesus, which could severely weaken them economically. The campaign was disastrous for Athens. By 413 Athens lost most of her army and fleet, and Sparta was encouraged to resume the war.
By now Sparta realized that they could not win the war so long as Athens controlled the sea. A deal was struck with Persia in which Persia assisted Sparta with the building of a fleet. In return, Persia was given control of Asia Minor. In 405 B.C. the Spartan fleet caught the unsuspecting Athenian fleet at Aegospotami in Thrace. The battle resulted in defeat for Athens and 160 of her 180 ships were captured or destroyed. In April 404 B.C. Athens surrendered and Sparta marched into Athens tearing down her walls.